(a) Field of the Invention
The present invention relates to a switch driving circuit and a switch driving method.
(b) Description of the Related Art
FIG. 1 is a schematic view of a circuit generating AC power through a switching operation of a conventional switch and supplying it to a load. An high-side switch Q11 and a low-side switch Q12 shown in FIG. 1 include an n-channel MOSFET. The drain electrode of the high-side switch Q11 is input with a predetermined power voltage Vdc, and the gate electrode is input with a gate signal HO. The drain electrode of the low-side switch Q12 is connected to a source electrode of the high-side switch Q11, and the source electrode is input with a ground voltage. The gate electrode of the low-side switch Q12 is input with the gate signal LO. The high-side switch Q11 and the low-side switch Q12 include body diodes D1 and D2, and the node of the source electrode of the high-side switch Q11 and the drain electrode of the low-side switch Q2 become an output terminal. An inductor L and the first resonance capacitor C1 are connected in series between the output terminal and the load Rx, and the second resonance capacitor C2 is connected to the load Rx in parallel. The inductor L and the first and second resonance capacitors C1 and C2 compose a resonance circuit along with the load Rx.
The above-described switch circuit is operated by a zero voltage switching control method. The zero voltage switching turns on the high-side switch Q11 and the low-side switch Q12 when the voltage difference between the drain electrode and the source electrode of the high-side switch Q11 and the low-side switch Q12 is about 0V, and thereby a conduction loss is decreased. However, when the resonance circuit is a capacitive load condition, the current of the inductor L is faster than the phase of the output voltage Vs. Thus, hard switching is generated. The hard switching means that the high-side switch Q1 (or the low-side switch Q12) is turned on when the voltage difference between the drain electrode and the source electrode of the high-side switch Q11 (or the low-side switch Q12) is high. Generally, if the hard switching is generated, the power loss of the switching element is increased, and the switching element is easily broken.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.